Candida albicans is an opportunistic pathogen that causes oropharyngeal disease in a large and diverse population of patients, including those with HIV/AIDS. Azole antifungal agents are the current mainstay of therapy for oropharyngeal candidiasis. However, because of the emergence of azole resistance, it is critical to develop novel strategies to prevent and treat this disease. Our goal is to identify new C. albicans virulence genes and to determine the mechanisms by which they contribute to pathogenicity. This information holds Dromise to identify new targets for antifungal strategies. During an oropharyngeal infection, C. albicans invades and damages oral epithelial cells. We have found that many C. albicans mutants with decreased virulence in the mouse model of oropharyngeal candidiasis also have reduced ability to invade and damage oral epithelial cells in vitro. Therefore, we hypothesize that the capacity of C. albicans to invade and damage oral epithelial cells is critical for the organism to establish and maintain an oropharyngeal infection. Our objective is to use in vitro studies of the interactions between C. albicans and oral epithelial cells to define mechanisms of host-pathogen interaction. Specifically, we will determine the mechanisms by which C. albicans invades and injures oral epithelial cells through the following aims. (1) We will identify the epithelial cell receptors that C. albicans uses to invade this host cell. (2) We will use our existing information on the transcriptional response of C. albicans to oral epithelial cells to identify C. albicans genes encoding potential virulence factors that are necessary for oral epithelial cell damage. The function of these genes will be investigated by constructing insertion and overexpression mutants. These mutants will be screened for their ability to damage epithelial cells in vitro. (3) Mutants with epithelial cell damage defects will be analyzed further by determining the epithelial cell receptors to which they bind, their ability to invade oral epithelial cells in vitro, and their virulence in the mouse model of oropharyngeal candidiasis. (4) The functional relationships among C. albicans virulence genes will be elucidated by transcriptional profiling and epistasis analysis using both newly created and existing C. albicans mutants.